The cheapest route is the Backcountry Camping in LBL - campgrounds with limited amenities. The campsites are great and will accommodate RVs, and your best shot at being on the water. I've always liked Smith Bay on KY, and Taylor Bay on Barkley.

LBL Backcountry Camping:
http://www.lbl.org/CAMPAreasLakeAccess.html

Some others you might look into:

KOA in Calvert City:
http://www.koa.com/where/KY/17130/

Hillman Ferry:
http://www.lbl.org/CAMPHillman.html